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How to Use the Refrigerant Charge Calculator
Select the refrigerant, the liquid line outside diameter and imperial (lb, ft) or metric (kg, m) units.
Enter the factory charge from the outdoor unit nameplate, the line set length that charge covers, and the actual installed liquid line length.
Enter the manufacturer correction factor per foot or metre. Leave it blank to use an estimate from the liquid line volume.
Add any indoor coil adjustment or the charge already in the system, calculate, weigh in the amount shown, then verify with superheat and subcooling.
How refrigerant charge weight is calculated
A split system leaves the factory charged for a set length of line set, and the nameplate says how long. A longer liquid line holds more liquid refrigerant than the factory charge accounts for, so you add the difference. The target charge is the nameplate charge, plus the extra line length times the correction factor, plus any indoor coil adjustment in the installation manual.
What the correction factor represents
The factor is the mass of liquid refrigerant in one unit of liquid line. It depends on the inside diameter of the tube and on the density of the liquid, so it changes with both line size and refrigerant. The calculator estimates it from the inside diameter of ACR copper tube and the saturated liquid density at 35°C. For R-410A that gives 0.20 oz/ft on 1/4 inch tube, 0.53 oz/ft on 3/8 inch and 1.04 oz/ft on 1/2 inch. For R-32 the same tubes give 0.18, 0.48 and 0.95 oz/ft, because liquid R-32 is about 9% lighter. Use the manufacturer figure whenever the installation manual gives one.
Where liquid density comes from
The densities behind the estimates are saturated liquid values from CoolProp, built from the component mixtures for the blends. For a pure refrigerant you can check them against the saturation tables in the NIST Chemistry WebBook entry for R-32, which gives saturated liquid density by temperature. A warmer liquid line holds slightly less refrigerant per foot, which is one reason published factors differ a little between manufacturers.
Imperial and metric units
Nameplates in Canada appear in both systems, and mini-split manuals list the extra charge in grams per metre. Switch the units selector and the fields convert in place, and every result shows both systems. If you need to convert a cylinder or scale reading on its own, the mass converter handles it. One ounce is 28.35 g and one foot is 0.3048 m, so 0.60 oz/ft is 55.8 g/m.
Weighing in and verifying the charge
Weighing in the target charge gets the system close, and measurement confirms it. Run the system at steady state and check superheat and subcooling with the superheat calculator and the subcooling calculator. For a full verification routine with airflow and temperature checks, use the refrigerant charge verification calculator. Charge blends such as R-410A, R-407C, R-454B and R-404A as liquid, and use the refrigerant blend calculator to see how much glide each one has.
Topping up after a repair
To find the top-up amount, subtract the charge still in the system from the target charge. If you recovered all of the refrigerant, the existing charge is zero and you weigh in the full target. If the result shows the system holds more than the target, recover the excess. Find and repair the leak before you recharge. R-22 is an ozone-depleting HCFC, and Environment and Climate Change Canada describes how the Ozone-depleting Substances and Halocarbon Alternatives Regulations control such substances, so confirm that supply and use are permitted before you specify it.
Flammable refrigerants and charge limits
R-32 and R-454B are class A2L. Equipment that uses them carries charge limits tied to the room or the installation, and the limit can be lower than the target charge for a long line set. The calculator reports the target charge only and does not check the limit, so read the installation manual before you add refrigerant to an A2L system.
Line length, lift and oil return
Every manufacturer publishes a maximum line set length and a maximum vertical lift for each model, and the charge correction only holds inside those limits. Long runs and large lifts also affect oil return on the suction line. Check the limits in the installation manual, and use the refrigerant piping calculator to check line sizes and velocities on long runs.
Frequently Asked Questions
Subtract the line set length covered by the factory charge from the actual liquid line length, then multiply the extra length by the correction factor. The Example button uses an R-410A system with a 6.5 lb nameplate charge, a 15 ft rated line set, 50 ft installed and a 0.60 oz/ft factor. The 35 extra feet add 21 oz (1.31 lb), so the target charge is 7.81 lb (3.54 kg). Check the nameplate value and correction factor against the installation manual.
Use both. Weighing in is the most reliable way to charge a new installation or a system that was fully recovered, because you know how much went in. Superheat and subcooling confirm that the charge is right for the actual airflow and load. Weigh in the target charge, run the system at steady state, then check superheat and subcooling and adjust in small steps by weight.
The estimate is the mass of liquid refrigerant in one foot of the liquid line, from the inside diameter of ACR copper tube and the saturated liquid density at 35°C. For R-410A on 3/8 inch tube it is 0.53 oz/ft, while published figures are often rounded up to about 0.6 oz/ft. Use the manufacturer value when you have it. The estimate is a check on the order of magnitude and a starting point for equipment without a published factor.
The Metric Example button uses an R-32 system with a 1.05 kg factory charge covering 7.5 m of pipe, with 12 m installed on a 1/4 inch liquid line. With no factor entered, the estimate is 16.8 g/m, so the 4.5 m of extra pipe adds 75.5 g and the target charge is 1.13 kg. R-32 is class A2L, and systems that use it have charge limits tied to room size, which this tool does not check.